Traumatic brain injury (TBI) is a serious public health concern. It is estimated that severe TBI will become the third most common cause of death and disability globally by the year 2020. An estimated 1.5 million persons sustain a TBI in the United States annually resulting in more than 230,000 hospitalizations and 50,000 deaths. The annual economic cost to society for the care of head-injured patients has been estimated to exceed $25 billion. In particular, there is a desperate need to have therapeutic agents available to treat head injuries that occur in large numbers among US troops engaged in combat. However, no truly efficacious and approved therapies are currently available for the treatment of TBI. Glutamate-receptor-mediated cell injury acts as an important mechanism of secondary brain damage after TBI. NAAG peptidases (GCPII and III) are extracellular enzymes that hydrolyze N-acetylaspartylglutamate (NAAG) to N-acetylaspartate (NAA) and glutamate (Glu) following the release of the peptide into the synaptic space. Inhibition of GCPII and III increases NAAG levels with the consequent activation of presynaptic group II mGluRs and inhibition of transmitter release including glutamate. These actions have the potential to provide neuroprotection in clinical conditions in which Glu mediates and mGluR3 activation reduces clinical pathology. To date, our research team has identified a number of urea-based compounds including ZJ 43, ZJ 11 and ZJ 17 as NAAG peptidase inhibitors with nM potency after extensive structure activity relationship studies. Data from animal studies have demonstrated that administration of ZJ 43 represents a potential novel strategy to provide neuroprotection after TBI. However, there exists an important concern that these compounds are too polar to readily penetrate the blood-brain barrier (BBB). The development of prodrugs will provide the means for precise dose delivery to the brain as well as the use of lower dose ranges that obviate the problem of unwanted systemic side effects. The long-term goal of this research project is to develop these NAAG peptidase inhibitors as novel therapeutics for TBI. In order to accelerate the development and application of these compounds for human clinical trials, the immediate goal of this research proposal is to develop novel prodrugs to improve the BBB penetration capabilities of our candidate NAAG peptidase inhibitors. It is noteworthy that our very recent preliminary data have demonstrated that one mono-ester prodrug of ZJ 43 is three-fold more active than the parent drug ZJ 43 in Fmr1 knockout mouse models of fragile X syndrome and autism. All these preliminary findings encouraged us to pursue extensive studies on the design, synthesis and pharmacological investigation of prodrugs of our NAAG peptidase inhibitors. Through funding from this two- year SBIR grant, we intend to bring our discovery of the efficacy of NAAG peptidase inhibitors in animal models of TBI to a higher level of preclinical development and ultimately to foster the translation of this concept into clinical trials. Specific Aim 1: Synthesis of compounds: Rational design and synthesis of new prodrug forms of lead NAAG peptidase inhibitors. Based upon the structures of our lead NAAG peptidase inhibitors and the successful results achieved for some commercial prodrugs, ten prodrugs including seven mono-ester or amide prodrugs and three 1,4-dihydropyridine prodrugs of the current best drug candidates ZJ 43, ZJ 11, and ZJ 17 will be synthesized for the testing described in Aim 2. In addition, 1.0 gram each of the above three parent NAAG peptidase inhibitors will be prepared as reference compounds for the studies of their prodrugs for the purpose of efficacy comparison. Specific Aim 2: Pharmacological studies of the above prodrugs: Testing of above compounds using an in vivo TBI model. The prodrugs identified in Aim 1 will be tested for cellular protection in a well- characterized and clinically relevant rat model of TBI. Each of the ten prodrugs from Aim 1 will be evaluated in a dose-dependent design in which drugs are administered systemically after TBI. Drug efficacy for reducing neuronal cell death will be evaluated at 24 hours after TBI using histofluorescence with advanced stereological cell counting techniques. The three most efficacious prodrugs for reducing acute cell death will be scaled up and undergo further in vivo functional testing to determine their efficacy for reducing motor and cognitive behavioral deficits associated with TBI. Key words: NAAG peptidase inhibitors, Traumatic brain injury, Head injury, Therapeutics, NAAG, GCP II, GCP III, Glutamate, Neurotransmitters, Excessive glutamatergic transmission, mGluRs, mGluR3, Prodrug, Mono-ester, Mono-amide, 1,4-Dihydropyridine, Drug delivery system, Blood-brain barrier, TBI model, CNS disorders, Neuroprotection.Traumatic brain injury (TBI) is a serious public health concern, and estimated to become the third most common cause of death and disability globally. Our proposal entails the chemical design and synthesis of novel NAAG peptidase inhibitors and their prodrugs, as well as in vivo TBI pharmacological studies of these compounds, which have the great potential to be developed as therapeutics for the treatment of traumatic brain injury.